Slip rings



A. s. CLARKE 2,959,697

SLIP RINGS Filed Sept. 15, 1958 Nov. 8, 1960 I0 [Ob I06 IO! IN VE N TOR ALFRED 6. CLAW/(505654559 BY LOR/VA CLARKE, EXECUTRIX 50g 6 BY A ATTOiQ/VEYSW United States Patent SLIP RINGS Alfred Gordon Clarke, deceased, late of Rexdale, On-

tario, Canada, by Lorna Irene Clarke, executrix, Acton, Ontario, Canada, assignor to Orenda Engines Limited, Malton, Ontario, Canada, a corporation Filed Sept. 15, 1958, Ser. No. 761,204

4 Claims. (Cl. 310-232) This invention relates to a slip ring assembly of the kind employed in conjunction with a brush or similar electrical collector to provide a continuous electrical circuit between two relatively rotatable members, and is specifically concerned with a slip ring assembly which is capable of withstanding high temperatures and the stresses imposed by high rotational speeds such as are commonly encountered in gas turbine engines.

The major problem encountered in the construction of such slip ring assemblies is the failure of available insulation materials to withstand high temperatures and the stresses imposed by high rotational speeds. Insulation materials commonly used for this purpose are epoxy resins, phenolic resins and tefions.

Since the insulation material invariably has to provide a support for the slip rings in such an assembly, the distortion of the insulation material under accelerations, of for example, 9000 G, such as commonly arise in gas turbine engines, results in movement of the slip rings relative to their axis of rotation, with consequent nonuniform motion of the surface of the slip rings relative to the brushes. This in turn results in brush bounce and a consequential lack of electrical continuity between the slip rings and their associated brushes, and also causes an out-of-balance of the rotating parts which has in the past been found suflicient to cause complete disintegration of the slip ring assembly.

An object of the present invention is to provide an improved slip ring assembly which is capable of withstanding high temperatures and high speeds of rotation.

A further object of the invention is to provide an improved method of manufacturing a slip ring assembly.

According to the invention the slip ringassembly includes a metal ring, and a continuous sheathing of an electrical insulating material which is chemically and physically stable at all temperatures at which the slip ring is to be operated which extends over and is bonded to a major portion of the surface of the ring in a continuous band which is a surface of revolution about the axis of the ring.

Preferably the electrical insulating material is a vitreous enamel, and, where the metal ring is formed from a metal of relatively poor electrical conductivity, preferably a continuous coating of a metal of lower specific resistance than the specific resistance of the metal of the ring is provided extending in a continuous band over the sired on the exposed surface of the metal ring with a metal of lower specific resistance than the specific resistance of the metal of the ring.

Other objects and advantages of the invention will become apparent from a study of the following specification when taken in conjunction with the accompanying drawings, in which:

Figure l is a fragmentary perspective view showing a portion of one construction of slip ring assembly according to the invention;

Figure 2 is a fragmentary perspective view of a portion of a modified form of slip ring assembly according to the invention; and, I

Figure 3 is a fragmentary sectional elevation showing two of the slip ring assemblies of the invention when cemented into a housing associated with a rotor structure of a gas turbine engine.

Referring to Figure 1, the slip ring assembly includes a metal slip ring 10 of silver alloy or steel, the ring having a groove 10a in its radially outer periphery 10b and a groove 10c in its radially inner periphery 10d for a purpose hereinafter explained.

Extending over the outer periphery 10b of the ring and over the surfaces providing the groove 10a, across one radial face 10 of the ring, and across the inner periphery 10d of the ring and over the surfaces providing the groove in a continuous band which is a surface of revolution about the axis of the ring, is a thin film 11, for example of 15 to 30 thousandths of an inch in thickness, of a vitreous enamel. The film of vitreous enamel is formed by fusing a slurry of vitreous alumina or porcelain powder onto the surface of the ring in a manner well known in the enameling art.

Where the ring 10 is formed from a metal of relatively poor electrical conductivity, for example from steel In use, a plurality of the slip ring assemblies described with reference to Figure 1 are formed of the necessary different diameters for them to nest one within the other with a slight clearance of, for example, 60 thousandths of an inch, and the series of assemblies are nested in a recess in a housing 13, such as is shown in Figure 3, and are cemented in place using a suitable cement such as that known under the registered trademark Saureisin, as indicated at 14 in Figure 3. Saureisin is a thermo-hardening resin having a setting temperature in the vicinity of 300 C.

The function of the enamel coating is to provide electrical insulation around the metal slip ring and enables the ring to be secured in place in an electrically-conductive housing by means of a fluid cement without the use of an external jig or fixture to keep the ring in place and out of contact with the housing. Also, the enamel coating on the ring enables the clearances between the respective slip ring assemblies and the housing to be kept to a minimum, thus minimizing the amount of cement which must be used to secure the assemblies in place, as such cements are mechanically weak.

It has been found that a slip ring assembly manufactured according to the invention, maintains its mechanical accuracy and stability at high temperatures, for example, at 200 C. operating temperature, and also at high rotational speeds since the enamel coating is found to adhere to the slip ring under all conditions so far encountered. A particular example of one set of operating circumstances where the slip ring assemblies of the invention have been found to perform satisfactorily is one where the maximum radius of the slip ring was seven inches,

the speed of rotation 8,700 rpm, and the operating temperature 200 C. Under these conditions the slip rings performed with complete stability and it was found there was no tendency for brush bounce to develop.

As will be apparent, the cement employed for securing the rings to the housing must be of a nature such that it does not deteriorate at the maximum operating temperature which is likely to be encountered. The cement given above as an example is found to meet these re quirements admirably.

Where it is anticipated that the maximum operating temperature will be substantially higher than 200 C., the construction shown in Figure 2 is preferably employed, the difierence between the construction shown in Figure 2 and that shown in Figure 1 being that subsequent to the formation of the coating of vitreous enamel, the enamel coating is given a coating of a slurry containing silver oxide, and then the slip ring assembly is heated in a reducing atmosphere to produce a dispersion of metallic silver particles 15 on the enamel coating and to sinter those particles to the coating. The slip ring assemblies can be soldered into their housing, using, for example, a solder containing tin, lead and silver and melting at a temperature lying in the range 500-600 C. The slip ring shown in Figure 2 may similarly be plated with metallic silver or an alloy of silver on its contact face, which plating is preferably performed after the formation of the dispersion of metallic silver on the layer of enamel in order that the particles may be built up into a substantially continuous film.

As will be appreciated, the specific embodiments of the invention described with reference to Figures 1 to 3 are to be taken by way of example only of one of the many forms the slip ring assemblies may take. For example, the contact face of the ring may be provided by the outer or inner surfaces, b, 10d, in which case the grooves 10a and 10b would be provided in the radial faces 102, 10 of the ring, and various ones of the faces of the ring may be of a different profile in order to accommodate specific requirements.

It is claimed:

1. A slip ring, including a metal ring, a continuous sheathing of an electrical insulating material which is chemically and physically stable at all temperatures at which the slip ring is to be operated extending over and bonded to a major portion of the surface of the ring in a continuous band which is a surface of revolution about the axis of the ring, a continuous coating of a metal of lower specific resistance than the specific resistance of the metal of the ring extending in a continuous band over the remaining portion of the ring and bonded thereto, and a coating of a metal having a melting point which is higher than any temperature at which the slip ring is to be operated extending over and bonded to a portion of the outer surface of the insulating material and electrically insulated from the coating of metal of lower specific resistance and from the ring itself by the sheathing of electrical insulating material.

2. A slip ring according to claim 1 in which the electrical insulating material is a vitreous enamel.

3. A slip ring according to claim 1 in which the continuous coating of a metal of a lower specific resistance than the specific resistance of the metal of the ring is metallic silver.

4. A method of manufacturing a slip ring, including the steps of applying a slurry of a heat-fusible electrical insulating material to a metal ring in a continuous band which is a surface of revolution about the axis of the ring, heating the ring and the applied slurry to a temperature sufficient to fuse the electrical insulating material in the slurry, electro-plating the exposed surface of the metal ring with a metal of lower specific resistance than the specific resistance of the metal of the ring, applying a slurry containing reducible oxide of a metal to a portion of the outer surface of the insulating material at a position isolated by the insulating material from the said electro-plated metal, and subsequently heating the ring in a reducing atmosphere to reduce the metal oxide and to sinter the metal particles thus formed to the insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,441,569 Fischer Ian. 9, 1923 1,721,515 Kroehle July 23, 1929 2,037,457 C'olson Apr. 14, 1936 2,060,480 Arnold Nov. 10, 1936 

